In the following, a tissue paper product relates to an absorbent paper based on cellulose wadding which is also called tissue paper base-sheet in this field of technology. A typical absorbent paper has a low basis weight, in the range from 10 to 50 g/m2.
The tissue paper can be produced from paper fibers according to the Conventional Wet Press (CWP) manufacturing method, or by the Through Air Drying (TAD) manufacturing method, or any alternative manufacturing method (e.g. Advanced Tissue Molding System ATMOS of the company Voith, or Structured Tissue Technology SST of the company Metso Paper). The paper fibers can be produced from virgin and/or recycled paper pulp raw material.
The CWP manufacturing method includes the steps of:                pressing and drying the wet paper fibers as a sheet on a large-diameter, heated cylinder (also called Yankee dryer); and        subsequently detaching and creping the sheet of dried paper fibers by means of a metal blade applied against said cylinder, across its direction of rotation.        
The creping operation creates undulations in the sheet across its direction of travel. The creping operation increases the thickness of the sheet, and confers elasticity and gives touch properties to the sheet.
The TAD manufacturing method includes the steps of:                molding the sheet of wet paper fibers on a fabric; and        subsequently drying the sheet, at least partly, by means of a current of hot air passing through it.        
Subsequently, the dried sheet may be creped.
Once, the tissue paper has been manufactured, a distinct manufacturing operation called converting operation is necessary to form the end product (i.e. the paper towel, toilet tissue rolls, bathroom tissue, wiping tissue, kitchen tissue rolls, handkerchiefs, etc. . . . ). During the converting operation, several of such sheets, also called plies, can be combined to form said end product.
It is possible to combine several plies together to confer particular properties on a sheet such as thickness, bulkiness, softness, and strength.
Several plies may be combined together by a combining operation of a chemical nature (e.g. by adhesive bonding), or of a mechanical nature (e.g. by knurling or embossing), or a combination of both. During adhesive bonding, a film of adhesive is deposited over some or all of the surface of one of the plies, then the adhesive-treated surface is placed in contact with the surface of at least one other ply. During the mechanical combination, the plies may be combined by knurling, or by compression, or by embossing. Embossing is a process by which a raised or depressed design is produced, generally by pressure between engraved rolls or plates or between an engraved roll or plate and an elastic or a deformable supporting surface. It results in a CWP ply having a particular relief or indentation. The thickness of the CWP ply or of the multiple plies is increased after embossing compared with its initial thickness.
In order to produce very soft multi-ply tissue paper product, for example toilet tissue comprising two TAD plies or TAD ply combined with one CWP ply, it was until now assumed that:                the TAD ply to be used should be as soft and smooth as possible,        the TAD ply should not be embossed or at least embossed as little as possible so as to preserve its properties, in particular thickness and strength during the converting operation, and        the TAD ply is already structured as a consequence of the manufacturing process (a face of the TAD ply reproduces the structure of the fabric supporting the wet paper fibers), and thus conferring an additional pattern to the TAD ply is not considered as desirable.        
In order to achieve a TAD ply of high softness and suppleness, it was commonly accepted to reduce the strength of the TAD tissue (for a given grammage) during the TAD manufacturing process (TAD papermaking machine), for example below 40 N/m CDT or 110 N/m MDT. Further, below a determined strength, the breaks of the TAD tissue increase significantly during the TAD manufacturing process. This may even reach the point where it is no longer possible to produce the TAD tissue. Furthermore, it is possible to reduce the number of TAD tissue breaks by reducing the speed of production of the TAD tissue by the TAD papermaking machine. Furthermore, it is possible to increase the TAD tissue strength by increasing the grammage. However, these solutions are difficult to implement within the frame of an industrial production of TAD tissue without negatively affecting productivity and cost of production.
The document WO 2011/069532 describes a fibrous product, especially tissue paper product, nonwoven product or a hybrid thereof, preferably hygiene and cleaning product, has at least one ply, the surface of which is partly covered with an embossing pattern, and is characterized in that the pattern comprises at least one first zone being micro-embossed with at least 30 embossing depressions per cm2, preferably 30 to 160 embossing depressions/cm2, more preferably 30 to 120 embossing depressions/cm2 and most preferably 45 to 100 depressions/cm2, forming a background embossing area, a plurality of second zones being unembossed and forming a motive element and in addition to the second zones at least one third zone being largely surrounded by linear depressions. The document also describes an embossing roll and an embossing device including a method for manufacturing such fibrous products. In this document, the micro-embossed zone results either by micro-embossing a creped tissue paper during a converting process or by using the intrinsic effect linked to the TAD process during the papermaking process.
The document WO 02/103112 describes a multi-ply tissue paper product and a method for producing same. The multi-ply tissue paper comprises at least three embossed plies of paper, wherein a first outer ply has a first microstructure pattern with first protuberances with a density of more than 40 protuberances/cm2. The second outer ply is provided with a second microstructure pattern also having a density of second protuberances of more than 40 protuberances/cm2. A middle ply is sandwiched between the first outer ply and the second outer ply and has a third structure pattern being an embossing pattern with a density of less than 40 protuberances/cm2. All three plies are ply bonded together after the first outer ply, the second outer ply and the middle ply have been structured separately. In this document, the TAD process is presented as an alternative to the micro-embossing of a tissue ply produced by a conventional wet press CWP manufacturing method.
The document WO 2011/035803 describes a fibrous product, especially tissue paper product, non-woven product or a hybrid thereof and preferably hygiene and cleaning product, comprising at least: one top ply with either an embossing pattern forming pillow-like chambers at least partially surrounded by first embossing protuberances or with second embossing protuberances; at least one middle ply embossed in register with the at least one top ply so that either second embossing protuberances of the at least one middle ply nest into the pillow-like chambers of the at least one top ply or second embossing protuberances of the at least one top ply nest into the pillow-like chambers at least partially surrounded by first embossing protuberances of the at least one middle ply; and at least one bottom ply not in register with the at least one top ply and being bonded to both the at least one top ply and the at least one middle ply. In this document, the TAD process is also presented as an alternative to the micro-embossing of a tissue ply produced by a conventional wet press CWP manufacturing method.
Thus, the above mentioned documents generally describe two main alternatives in order to micro-structure a ply, either by micro-embossing a classical CWP type ply or by manufacturing the ply by a TAD process.
There is a need to improve the suppleness and softness of the multi-ply tissue products. Further, this should be obtained in economical or cost effective manner.